Coded railway signaling system



Dec. 10, 1957 c. D. IHRIG GODED RAILWAY SIGNALING SXWSTEM Filed Dec. 21, 1953 `United States Patent O CODED RAILWAY SIGNALING SYSTEM Clitord D. Ihrig, Penn Township, Allegheny County, Pa.,

assigner to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application December 21, 1953, Serial No. 399,426

1 Claim. (Cl. 246-34) My invention relates to coded railway signaling systems, and particularly to an improved arrangement `for supplying coded energy in a coded railway signaling system for the control of cab signals and/or speed control equipment on Vehicles traveling through a stretch of track equipped with apparatus embodying my invention.

In conventional coded railway signaling systems, energy coded at one or another of several different rates, say, for example, 180 or 75 times per minute, is supplied to the rails of a stretch of track at the exit end thereof, and flows over the rails to apparatus located at the entrance end -o'f the stretch, which apparatus is selectively responsive to the reception of impulses of energy at the various code rates to thereby control wayside signals or other traic controlling devices. Continuous inductive cab signals or automatic speed control `for vehicles which travel over the stretch may be provided by employing alternating c-urrent energy for the trackway codes, and .providing suitable apparatus on the vehicles for detecting the presence of such codes in the track rails of the stretch over which the vehicle is traveling. Such carb signal apparatus is usually arranged so that the 'ca-b signal aspect repeats the aspect of the Wayside signal previously passed by the train. That is, when a train passes a signal displaying a green or clear aspect, coded energy at a particular rate, say, for example, 180 times per minute, is being supplied to the rails of the stretch at the exit end thereof. The reception of code at the 180 code rate by the train-carried apparatus will cause the calb signal apparatus to display a green or clear aspect. If the train passes a signal displaying a yellow or approach aspect, the apparatus is usually arranged so that coded energy at the 75 code rate is supplied to the rails of the stretch in advance of the signal, so that the cab signal apparatus will display a yellow or approach aspect in t-he cab of the vehicle. The presence of steady energy, the absence of energy, or the presence of energy at a frequency which is inelfective to operate the cab signal apparatus will each cause the cab signal to display a restrictive or caution aspect. It -will accordingly be seen that when a train passes a wayside signal displaying an approach aspect with the signal in advance displaying a red or stop aspect, the cab signal apparatus 4will continue to display a yellow or approach aspect throughout the entire length of the stretch. It is sometimes tpreferred to provide what is known in the railway signaling art as a code change point at an intermediate point in the track stretch between wayside signals so that energy coded at the 75 code rate may be supplied to the rails of the lsection from the code change point to the signal in the rear, but steady energy or no energy is supplied to the section in advance of the code change point, that is, the section between the code change point and the signal in advance.

Such an arrangement is particularly useful for wayside signals which display an absolute stop aspect, requiring all trains to come to a stop and remain stopped v as long as the signal displays its stop aspect. With such 2,816,219 Patented Dec. 10, 1957 an arrangement, if the wayside signal is displaying its stop aspect, the next signal in the rear will display its approach aspect. A train passing the next signal in the rear Iwill receive code energy, and accordingly an approac-h cab signal aspect will -be displayed, until the train passes the code change point, at which time the cab signal will operate to display its restrictive or caution aspect, thus giving additional warning to the engineman that he Iis approaching an absolute stop signal. Under such circumstances, the apparatus must be arranged so that, -when the signal in question displays a clear or approach aspect, energy coded at the code rate will be supplied to the rails of the section immediately in the rear of the signal, and will ibe cascaded at the code change point intermediate in the stretch, so that the section in the rear of the code change point is also supplied Iwith energy coded at the 180 code rate. However, when the signal in question is at stop, the apparatus must ybe arranged in such manner that, lwhile a train is in the rearmost section of track, that is, the section between the code change point and the next si-gnal in the rear of the signal in question, energy at the 75 code rate will be supplied to the rails `of the stretch between t-he signal in question and the next signal in the rear and no energy will :be supplied to the track while a train is in the section extending between the code change point and the signal in question.

Although a number of methods have 'been .proposed in the past for providing such operation and providing suitable equipment for use with code change points, such apparatus usually has the disadvantage of requiring line wire control circuits extending between the signal locations and the code change point location.

Accordingly, it is an object of my invention to provide an improved coded railway :signaling system, arranged to provide a code change point location in a stretch of track extending between two wayside signal locations, with the apparatus arranged so as to require no line wire fin the areas -between either of the signal locations and the code change point location.

Another object of my invention is to provide an irnproved coded railway signaling system in which a code change .point is provided at an intermediate point in a stretch of track between two wayside signals, the control of the apparatus being provided by the use of energy having different frequencies supplied to the track rails, one frequency of which is effective to govern wayside and cab signal apparatus of vehicles moving over the stretch; the other frequency, employed Ifor controlling the energy having the first frequency, ibeing of such frequency so as to be ineffective to operate the wayside apparatus or train-carried apparatus.

A further object of my invention is to provide a railway -signaling system in which, at a code change point, coded energy at a given frequency, ineiective to operate Wayside or cab signal apparatus, is continuously supplied to the rails and transmitted therethrough to the exit end of the section, where the reception of this energy causes the supply of energy, effective to operate cab signaling or wayside signaling apparatus, from the exit end of the section to the code chan-ge point where it is received and retransmitted to the section in the rear of the code change point to operate cab signal or wayside signal apparatus.

Other objects of my invention and features of novelty thereof will become apparent from the following description taken in connection with the accompanying drawing. y

ln practicing my invention, I provide, in a coded railway signaling system using trackway codes of alternating current having a given frequency for the control of cab signal equipment of trains which move through a section stop aspect.

of track, apparatus which transmits energy from the normal entrance end of the section to the normal exit end of the section. This energy is of a type which is not Yeffective to operate the wayside or train-carried signaling equipment. The reception of this energy at the lexit end of the section governs suitable means for controlling the supply ofthe trackway code to the rails of the section at the exit end thereof.

vIn ka preferred embodiment of my invention, the energy having the second frequency is supplied by a shockeXcited tuned circuit which supplies impulses of energy, at a second frequency ineffective to operate the wayside or train-carried coded signaling apparatus, to the rails of a section of track at the 'entrance end thereof. At 'the Jvexit end of the section, I provide code impulse receiving apparatus which is responsive only to energy impulses having the second frequency. Accordingly, when no train -is `occupying the section, the code responsive apparatus at the exit end of the section 'will be energized. Under these conditions, the code impulse receiving apparatus is controlled 'to supply trackway code at the first, or effective frequency, to the rails of the section at the exit end, in accordance with traffic conditions in advance of the section. However, if a train occupies the section, the code responsive means at the exit end of the section will be deenergized. The code responsive means is arranged to govern the transmission of the trackway code in such man- -ner that, when the code responsive means is deenergized,

the character of the ltrackwaycode is changed from a condition of low code rate to no code, to thereby lcause the icab signal apparatus to display Vits most restrictive or caution aspect, provided that traffic conditions in advance of the section are such that lthe most restrictive aspect should be displayed.

The single accompanying drawing is a diagrammatic View of a stretch of railwaytrack equipped with a signaling system embodying my invention.

Referring to the drawing, there is shown a stretch of railway track extending -between two wayside signals '1S and 2S, and divided `into a rearward section designated by the reference character -IAT and a forward section designated by the reference character IBT. The wayside signals IS and 2S govern -the movements of traic through the stretches in advance'of the respective signals, signal 1S governing the movement of traffic into ythe stretch including sections IAT and IBT. The signals may be `of any of the well-known types, andas here shown, signal 1S is a color light type of signal having a green lamp G which when lighted provides a clear aspect, 'a yellow lamp Y which when lighted provides an approach aspect, and a red lamp R which when lighted provides a The arrangement for governing the lamps of signal 2S is not shown in the drawing, since 'itis not essential to an understanding of my invention, and'may be arranged in a manner similar to that shown forsiglnal 1S.

As indicated by the arrow in the drawing,'traic normally moves through the stretch of track including rsections 1AT and IBT in the direction from left to right. It is assumed that vehicles or trains moving through this stretch are equipped with cab signal or train control apparatus of the type well known in the art, which cab signal apparatus responds, through the medium of inductive pickup apparatus on the vehicle or train, tothe presence of alternating current energy of a predetermined frequency supplied at different code rates to the section rails. A detailed description of the vehicle-carried apparatus is not included herewith, since this apparatus may be any one of a number of suitable types, and may be,

for example, of the type shown and described in Letters Patent of the United States No. 2,462,454, issued to Lesalternating current energy having a frequency of 100 cycles per second and supplied to the rails of the track stretch at the rate of 180 times per minute will cause the display of a clear aspect on the cab signal apparatus, whereas the presence of 100 cycle per second energy in the rails coded at the code rate will cause the display of an approach aspect on the cab signal apparatus, and the presence of steady energy having a cycle per second frequency, or the absence of any energy will cause the apparatus to display a `more restrictive aspect in the cab of the vehicle or train. It is also to be pointed out that the vehicle-carried apparatus will not respond to any coded energy other than that having 'the 100 cycle per second frequency.

The apparatus located at the first signal location, that is, the location of signal 1S, includes a code following track relay IATR connected across the rails of section IAT through a 100 cycle filter, which filter is constructed and arranged in the usual manner so that only alternating current energy having a frequency of 100 cycles per second can besupplied therethrough to operate the relay IATR. For detecting the code following operation of the relay IATR, there'is .provided a decoding transformer 1DT,`which governs the operation of a signal control reylay IHR, land also governs a clear signal control relay IDR through ya decoding unit DU, the relays IHR and IDR governing the aspect displayed by the wayside signal 1S. Atthefcode change tpoint, located at a point intermediate inithestretch,and at the point of adjacency of the ftrack sections IAT` and yIBT, there is provided a which is governed by aback contact of the track relay -1BTR. At the code change point,rthere is alsoprovided a staticv code alternator CA,fthe detailed description of 'which will y15e-'provided later, `which is governed by a cod- Eing-device y75CT so that thecode alternator continuously supplies-fimpulsesofenergy ata particular frequency, in

4thisiinstanc'e, 140 cycles per second, to the rails ofsec- 7tio`n-1BTatthe code-'change' point location.

At the seco'ndvsig'nal location, there is provided a track A'transformer -IBTT having alsecondary winding connected across the section'y rails of'section IBT through a reactor LI, andhav'ing aprimary-winding which is supplied with coded energyhaving a frequency of 100 cycles per second b'y a-circuit whichlis governed by the signal control frelay52HR,-which' relay 'is governed by traffic conditions in advance 'of signal `2S. The supply of 100 cycle coded energyto-'theptimary winding'of transformer 1JLBTT is additior'i'allygoverned` by the contacts of a coding device 'fCT'lanid a' coding d`evice180CT,v these' coding devices 'having contacts' *which are recurrently operated at the rates "of `7.5 and yi180 times "per minute, respectively.

Additionally,'at'the'second signaldocation, there is provided -anapproach 'codefollowing relay ZAV/R, connected to therails of jse'ction IBT through a 140 cycle filter arvrangedland vdispo'sed in such manner that only energy 'having' a frequency 'of l140 cycles per second will be passed bythe iilteritocauseopera'tion of the contacts of relay lZAVR. The'code'following operation of relay'2AVR 'is detected by an approach detector relay AVPR, which 'is'recurrentlysupplied"with energy from a decoding capacitor 'AVQ, and the contacts of relay AVPR are utilized ,'togovern the supply of coded energy to the rails of section '1'BT.

Energy 'for 'the operation of various of the relays is furnished by ya suitable lsource of low voltage' direct current, 'suchas'theb'attery LBv shown,l having its positive Vte'rriiinal ldesifg'nat'ed" by 'the reference lcharacter' B and its pegative' terminal designated by the reference character N. 75

It "is 'to be understoodthat such a source is provided at each of the three locations shown on the drawing. The 1GO cycle energy supplied for the operation of the coded track circuits and the cab signal equipment on trains moving through the stretch is supplied from a suitable source of alternating current energy having terminals designated by the reference characters BX100 and NX100, respectively, and it is to be understood that'such energy may be furnished through the medium of a suitable transmission line extending along the stretch of track.

It is believed that a better understanding of my invention may be had by a detailed analysis of the operation of the arrangement shown in the drawing under various traic conditions.

Considering first the normal condition of the apparatus, as shown in the drawing, the track sections lAT and lBT are unoccupied, and the signal control relay ZHR is picked up in accordance with traffic conditions in advance of signal 2S, so that signal 2S will display a clear aspect by the operation of circuits which, although not shown, may be similar to those shown for governing the lamps of signal 1S. At this time, with relay ZHR picked up, a circuit is established for supplying coded energy to the primary winding of the transformer lBTT, which circuit may be traced from terminal BX100 at contact a of the ltlCT coding device, over front contact a of relay o EHR, and through the primary winding of transformer IBTT to terminal NXltlll. The impulses of 100 cycle energy supplied 180 times a minute to the primary Winding of transformer ItBTT cause corresponding impulses of energy to be supplied from the secondary winding of this transformer through the reactor Ll to the rails of section lBT. At the code change point, the impulses of l0() cycle energy are passed by the 100 cycle lter and cause the recurrent operation of the contacts of relay llBTR at a corresponding rate, namely, 180 times per minute. Each time that contact a of relay IBTR is released, an obvious circuit is established for supplying energy to the winding of the slow release back contact repeater relay lBTP, so that at this time relay IBTP is picked up, and since the relay is of the slow release variety, its contacts will remain picked up during the short intervals in which contact a of relay llBTR is not in its released position. Each time that contact b of relay lBTR is picked up, a circuit is established for supplying impulses of 100 cycle energy to the primary winding of transformer lATT, which circuit may be traced from terminal BXlfltl at front contact a of relay lBTP, over front contact b of relay lBTR, and through the primary winding of transformer IATT to terminal NXltM). Accordingly, it will be seen that impulses oflOO` cycle energy are supplied to the rails of section llAT in step with the impulses of 100 cycle energy received from section IBT, the apparatus in this instance functioning in the usual manner of a front contact code repeating cut-section. At the entrance end of section IAT, the 100 cycle impulses are passed by the 100 cycle lter and cause the recurrent operation of the contacts of track relay lATR at the rate of 180 times per minute.

The recurrent operation of Contact a' of relay lATR `causes the supply of direct current energy alternately to tne upper and lower halves of the primary winding of the decoding transformer lDT, and the energy thus induced in the secondary winding of the transformer is mechanically rectified by the recurrent operation of contact b of relay IATR, the rectified energy being supplied to the winding of the signal control relay IHR. Accordingly, relay Alll-1R is picked up at this time. Additionally, energy is supplied by recurrent operation of contact a of relay IATR to the 180 decoding unit ISDU, and since the contacts of relay lA'IR are operating at the l() code rate, `sufficient energy will be passed by the decoding unit lltlDU to the winding of relay IDR to pick up the contacts of this relay. With the contacts of relays lHR and lDR both picked np, a circuit is es- 6 tablished for supplyingenergy to the green lamp G of signal 1S, which circuit may be traced from terminal B at front contact a of relay lHR, over front contact a of relay lDR, and through the green lamp G of signal 1S to terminal N. The signal 1S is accordingly displaying a clear aspect at this time.

At the code change point, the 75CT coding device is recurrently operating its contact a at the rate of 75 times per minute, and each time that the contact a of coding device 75CT is closed, energy is supplied to the 140 cycle static code alternator CA by the circuit which may be traced from terminal B at front contact a of the coding device 75CT, through the primary winding of the code alternator transformer to terminal N. The code alternator may be constructed and arranged in the manner shown and described in detail in Letters Patent of the United States No. 2,348,525, issued on May 9, 1944, to Austin M. Cravath, for Apparatus for Generating Coded Alternating Current. It is deemed sucient for the purposes of this disclosure to point out that the equipment is arranged so that the supply of direct current energy to the primary winding of the code alternator transformer causes the build-up lof energy in the magnetic field of the transformer, and when the contact a of coding device 7SCT interrupts the supply of direct current energy to the primary winding of the transformer, the magnetic field collapses, and with the capacitor shown connected across the primary winding of the transformer properly proportioned, the circuit will oscillate at a rate determined by the parameters of the circuit. It will be assumed in the present case that the apparatus is arranged so that, each time that contact a of coding device 75CT opens, a damped train of oscillations having a frequency of 140 cycles per second will be set up in the resonant circuit of the code alternator, which energy is supplied to the rails of section lBT by the connections from the secondary winding of the code alternator transformer. Accordingly, it will be seen that the rails of section lBT are continuously supplied with damped impulses of 140 cycle energy occurring at a 75 code rate, these impulses being supplied to the section rails at the code change point. At the exit end of section 1BT, the impulses of 140 cycle energy are supplied through the 140 cycle filter to the approach code following relay ZAVR, so that the contacts of this relay are recurrently operated at a 75 code rate by the 140 cycle energy supplied from the opposite end of the section. The code following operation of the contacts of relay ZAVR is detected by a circuit which includes the capacitor AVQ, which is connected across the direct current source each time that contact a of relay ZAVR is picked up, the capacitor being connected across the Winding of the approach detector relay AVPR each time that contact a of relay ZAVR is released, so that the capacitor discharges the energy through the winding of the relay AVPR. Relay AVPR is sufficiently slow in releasing its contacts so that with the contact a of relay ZAVR recurrently operating, the relay AVPR will remain picked up during the short intervals in which no energy is being supplied to its winding. Accordingly, it will be seen that when relay ZAVR is operating its contacts at the 75 code rate, relay AVPR will be picked up. It is to be noted that the reactor L1 in the circuit for connecting the secondary winding of transformer BTT across the rails of section IBT will retardthe flow of the 140 cycle energy through the secondary winding of the transformer, thereby reducing the shunting eect of the secondary winding of this transformer on the 140 cycle energy.

Because of the presence of the cycle lter in the connections of the winding of track relay IBTR to the rails of section 1BT, the track relay IBTR will be unaffected by the impulses of cycle energy supplied to the rails of the section at that end. Similarly, at the exit end of section 1BT, the presence of the 140 cycle filter in the connections of the winding of relay ZAVR to the rails of section 1BT will prevent the operation of relay AVR by the impulses vof 100 cycle energy supplied from the secondary winding of `transformer IBTT. Y

l With the apparatus Ain its normal condition as described above, with signals 2S and 1S displaying a clear aspect, 100 cycle energy coded at the 180 code frate present in both sections 1AT and IBT, it will now be assumed that a train 4moving "from left y'to `right passes signal 1S and enters section IAT. The 'shunting lelectA of the wheels and axles ofthe train in section IAT will 'cause 'relay IATR to release and 'remain released, so that the supplyof energy to 'relays IHR a'nd IDR is interrupted and these relays will release after Va short 'time interval. With contact a 'of relay `IHR released, the 'circuit previously ytraced for supplying energy to the green lamp G of signal IS is interrupted, and an obvious circuit is established over back contact a of relay IHR for supplying energy to the red lamp R'of signal 1S, so that signal 1Sn displays a red or stop aspect. Y

rOn the train, the train-carried cab signal equipment vwill pick up impulses of the l'0cyc1e energy inthe rails of section IAT,which is liowing through the section through the wheels vand axles "of the train, and the energ thus induced in the pickup coils of the train-carried equipment will cause the operation of the'cab signal apparatus to display a clear aspect on the cab signal lof the vehicle. When the train moves into section I-BT, the shunting elect of the wheels and axles of the train will cause relay IBTR to release and remain released, so that its front contact b interruptsithe vsupply of energy to the winding of transformer 1ATT,so that 100 cycle energy is no longer supplied to section 1AT at this time. The lOO cycle energy supplied to the rails of section IBT from the secondary winding of transformer IBTT will cause the cab signal apparatus to indicate a clear aspect on the vehicle, as the vehicle traverses section IBT. Ad-

ditionally, the presence of the train in section 1BT will shunt the supply of impulses of 140 cycle energy supplied from the code alternator at the code change point, so that energy will no longer be supplied to the winding of relay ZAVR and its contact a will release and remain to section IAT will continue lto be cut olf, since relay l IBTR will remain released at this time because of the presence of the train in section IBT. Accordingly, relay IATR will continue in its released position, and the relays IHR and IDR will both be released so that signal IS continues to display its red or stop aspect. The cab signal apparatus on the locomotive or vehicle moving through section IBT will continue toibe operated'by the energy induced in the vehicle pickup coils as the result of the l0() cycle energy Supplied to the rails of section IBT from transformer IBTT, until the train passes signal 2S and moves out of the section.

When the train passes signal 2S, relay ZHR will be released, it being assumed that relay ZHR for signal 2S is governed in a manner similar to that described for relay IHR associated with signal 1S. The release of contact a of relay ZHR interrupts the previously traced circuit for supplying 100 cycle energy coded at the 180 code rate to the primary winding of transformer 'IBTT and transfers the connection of the primary winding of transformer IBTT to a circuit including Contact a of the coding device 7SCT and front Contact a of relay AVPR. Since relay AVPR is dee'nergized at this time with the rear of the train occupying section IBT, no energy will be supplied to the primary winding of transformer IBTT.

When the rear ofthe train has passed signal 2S, so that section IBT is unoccupied, the 140 cycle energy supplied from the code alternator at the code change point willnow be effective to operate 'the `relay ZAVR, so that relay AVPR will close its front contacts. With contact a of relay AVPR picked up, a circuit is established for supplying energy to lthe primary winding of transformer lBTT, which circuit may be traced from terminal BXIO at front contact a of relay AVPR, over contact tz of coding device CT, over -back contact a of relay -2HR, and v'through the primary winding of transf'ori'ner -BTT to terminal NX-IGO. Accordingly, 100 cycle energy coded at the 75 code rate will'now be supplied tov the rails of section IBT 'at 'the exit end thereof. This cycle energy will llo'w over the section rails and cause operation of the contacts of relay IBTRfat the 75 'code rate. Each time that front Contact b of relay IBTR picks up, 100 cycle energy is supplied to the primary winding of transformer IATT by the circuit previously traced. Thus, 100 cycle energy coded at the 75 code rate is supplied to the rails of section 1AT at the code change point, and ows over the rails of section 1AT to cause `operation of the contacts of relay IATR at the entrance end of section IAT, at the corresponding 75 code rate.

With the contacts a and b of track relay IATR recurrently operating at the 75 kcode rate, energy will be supplied to the winding of relay IHR so that this relay will pick up its contacts. "However, insufficient energy is supplied to the decoding unit 180DU to pick up the contacts of relay IDR, so that relay IDR remains released at this time.

With relay IHR picked up and relay 1DR released, a circuit is established for supplying energy to the yellow lamp Y of signal 1S, which circuit may be traced 'from terminal B at front contact a of relay IHR, over back contact a of relay IDR, and through the yellow lamp Y of signal '1S to terminal N.

From the foregoing, it will be seen that at this time, with the signal l2S displaying a stop aspect because of the tratc conditions in advance causing the release of relay ZHR, the rails of the sections 1AT and IBT will be supplied with l0() cycle energy coded at the 75 code rate, and the reception of the 100 cycle energy coded at this rate at the location of signal 1S will cause this signal to display a yellow or approach aspect.

Let it now be assumed that, with signal 2S at stop and signal IS displaying an approach aspect, 'a train moving from left to right passes signal 1S and enters section 1AT. As previously pointed out, the shunting 'effect of the wheels and axles of the train in section IAT will cause the track relay IATR to release and remain released,

resulting in the subsequent release of signal control relay IHR, so that the yellow lamp Y of signal 1S is extinguished and energy is supplied to the red lamp R of the signal, so that the signal displays a red or stop aspect to the rear of the train. The 100 cycle energy supplied to the rails of lsection IAT and coded at the rate of 75 times a minute Will be picked up by the cab signal apparatus on the locomotive of the train, to thereby cause the cab signal to display an approach aspect. When the front of the train passes the code change point and enters section IBT, track relay IBTR is shunted and its contacts release and remain released so that the supply of energy to transformer IATT is cut off. Additionally, at this time, the supply of cycle energy from the code alternator CA to the rails of section IBT is shunted by the wheels and axles of the train, so that at the exit end of the section, relay ZAVR releases and remains released, which in turn releases approach detecting relay AVPR.

Upon the release of relay AVPR, the circuit previously traced for supplying energy to transformer IBT'I is interrupted, so that the supply of 100 cycle energy at the rate of 75 times per minute to the'rails of section IBT at the exit end thereof is discontinued at this time.

Since 100 cycle energy is no longer supplied to the rails .of section IBT, the cab signal apparatus will be operated to display its most restrictive aspect, to thereby indicate to the engineman that a Astop signal is being 'i approached.

When the rear of the train vacates section IAT, the supply of energy to the rails of section IAT from transformer IATT remains interrupted, since contact b of relay IBTR will continue to be released. Accordingly, signal IS will continue to display a stop aspect.

Let it now be assumed that tratiic conditions in advance of signal 2S become such that relay ZHR picks up. With contact a of relay ZHR picked up, the circuit previously traced for supplying l0() cycle energy coded at the rate of 180 times per minute to the winding of transformer IBTT is again established, so that energy coded at this rate is supplied to the rails of section IBT. Accordingly, the cab signal apparatus on the train occupying section IBT will respond to provide a clear or proceed aspect in the cab on the locomotive.

When the train in question passes signal 2S and the rear of the train vacates section IBT, the 100 cycle energy supplied at the exit end of the section will ow over the section rails to recurrently energize relay IBTR at the code change point, at the rate of 180 operations per minute. As a result, relay IBTP is again picked up and the circuit for supplying energy at the 180 code rate to transformer IATT is again established, so that relay IATR at the entrance end of the section IAT is again operated at the 180 code rate.

Operation of the contacts a and b of relay IATR at the 180 code rate results in the picking up of relays IHR and IDR, so that the circuit previously traced for supplying energy to the green lamp G of signal IS is again completed with the result that signal 1S again displays a clear aspect.

At the code change point, the supply of 140 cycle energy from the static code alternator will feed over the section rails `of `section IBT to recurrently energize the contacts of relay ZAVR at the exit end of the section, with the result that relay AVPR is again picked up. Accordingly, it will be seen that the apparatus is now restored to its normal condition as shown in the drawing.

From the foregoing description, it will be seen that my invention provides an arrangement in which the use of line wires to govern the supply of coded energy to the forward section of the two track sections of a stretch is eliminated, but the system provides the essential requirement of causing the supply of coded energy to be cut olf from the exit end of the forward section when a train enters the section and the signal in advance is displaying a stop aspect, so that the cab signal apparatus on the train or vehicle entering the section will display a restrictive aspect.

It will be obvious to those skilled in the art that other sources of energy may be used for providing the coded energy at the second frequency, other than the code alternator herein shown and described, the only requirement being that the frequency so generated is sufliciently different from the frequency of the energy effective to operate the cab signal equipment that no mutual interference takes place.

Although l have herein shown and described only one form of coded railway signaling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claim without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

In combination, a stretch of railway track over which trains equipped with cab signal apparatus responsive to alternating current of a rst frequency coded at one or another code rate move in one direction, said stretch being divided into two sections to form a code change point; a wayside signal governing the entrance of trains into said stretch, a signal control relay at the exit end of the forward section, said relay having a first and a second contact closed accordingly as the track stretch next in advance is unoccupied or occupied; means for continuously supplying to the rails of said forward section adjacent the entrance end thereof coded alternating current having a second frequency different from said first frequency and incapable of operating cab signal apparatus, means at the exit end of said forward section responsive to alternating current of lsaid second frequency and including a third contact closed only when said forward section is unoccupied, means controlled by said rst contact for supplying to the rails of said forward section alternating current of said rst frequency coded at said one code rate, means controlled by said second and third contacts for supplying to the rails of said forward section at the exit end thereof alternating current of said first frequency coded at said other code rate, means at said code change point responsive to the coded alternating current of said first frequency supplied to the rails of said forward section for supplying to the rails of the rear section alternating current of the same frequency coded at the same code rate, and means for controlling said wayside signal vby the coded alternat- 1ng current supplied to the rails of the rear section.

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